Process for tanning with a multivalent metal and an organic compound

ABSTRACT

A process for tanning hides or skins comprises firstly treating the hide or skin with a basic salt of a multivalent metal, secondly treating the hide or skin under alkaline conditions with an organic compound having a long chain aliphatic group and at least one reactive group capable of entering into a complex with a basic salt of a multivalent metal, and thirdly treating the hide or skin with a salt of a multivalent metal.

United States Patent 1191 Briggs 1*Mar. 11, 1975 I PROCESS FOR TANNING WITH A MULTIVALENT METAL AND AN ORGANIC COMPOUND [75] Inventor: Philip Stanley Briggs, Leeds,

England [73] Assignee: National Research Development Corporation, London, England 21 Appl. No.: 165,725

[30] Foreign Application Priority Data July 24, 1970 Great Britain 35994/70 [52] US. Cl. 8/9426, 8/9429 [51] Int. Cl. C14c 3/04 [58] Field of Search 8/9426, 94.29, 94.22, 8/9423 [56] k References Cited UNITED STATES PATENTS 2,178,874 l1/1939 Hervey 8/9426 2,693,996 1l/1954 Von Fuchs 8/9422 2,950,950 8/1960 Plapper et a1 8/9423 3,010,780 11/1961 Plappcr et al.... 8/9426 3,811,832 5/1974 Briggs 8/9426 FOREIGN PATENTS OR APPLICATIONS 788,539 171958 Great Britain 8/9422 836,808 6/1960 Great Britain 8/9426 OTHER PUBLICATIONS Revue Technique des Industries du Cuir, Sept. 15, 1955, page 205.

Revue Technique des lndustries du Cuir, February 1953, page 30.

Primary Examinr-Thomas J. -Herbert, Jr. Attorney, Agent, or Firm-Finnegan, Henderson. Farabow and Garrett 57 ABSTRACT A process for tanning hides or skins comprises firstly treating the 'hide or skin with a basic salt of a multivalent metal, secondly treating the hide or skin under a1- kaline conditions with an organic compound having a long chain aliphatic group and at least one reactive group capable of entering into a complex with a basic salt of a multivalent metal, and thirdly treating th hide or skin with a salt of a multivalent metal.

31 Claims, N0 Drawings PROCESS FOR TANNING WITH A MULTIVALENT METAL AND AN ORGANIC COMPOUND This invention relates to the production of leather.

In US. application Ser. No. 132,580, filed Apr. 8, 1971, and now U.S. Pat. No. 3,811,832 there is described and claimed a process for the tanning of a hide or skin by treatment with a basic salt of a multivalent metal, and then with a reaction medium containing a water-soluble salt of a dibasic organic acid, said watersoluble salt being one that forms an alkaline solution in water,'in an amount sufficient to maintain an alkaline pH in the reaction medium.

Leather which has been treated with a basic salt of a multivalent metal, that is mineral tanned, has a pH in water in the range 3 to 5. The effect of adding a salt of a dibasic organic acid is to raise the pH to within the range 7.5 to 8.5. Such conditions are well outside the normal practice in the tanning industry. It has now been found that, provided the alkaline conditions are maintained, certain other organic compounds can also usefully be employed in the above-mentioned process. The resulting leathers on re-tanning are found to have improved hydrophobic properties.

According to the present invention a process for the tanning of a hide or skin comprises firstly treating the hide or skin with a basic salt of a multivalent metal, secondly treating the hide or skin under alkaline conditions with an organic compound having a long chain aliphatic group and at least one reactive group capable of entering into a complex with a basic salt of a multivalent metal, and thirdly treating the hide or skin with a salt of a multivalent metal.

Treatment with the organic compound is preferably carried out at a pH from 7.5 to 9. An aqueous solution of the organic compound is prepared and adjusted to the required pH by addition of suitable organic bases or inorganic alkalis. The alkali or base need not react with the organic compound, and weak alkalis such as sodium carbonate or ammonia have been found to be particularly suitable. It is usually found that the optimum value'of pH is around 8.2 to 8.5. Preferably the leather is washed and neutralised throughout its whole thickness after tanning with the basic salt of a multivalent metal and prior to treatment with the organic compound, for example, with a weak alkali such as sodium bicarbonate, ammonium bicarbonate, ammonia or mixtures thereof. This neutralisation may be preceded by treatment with a salt of phthalic, formic or other weak acid.

The process of tanning with a basic salt of a multivalent metal can be carried out on stock with the hair or wool intact, or on hides and skins that been suitably prepared for tanning by conventional pre-tanning process, or that have previously been tanned, for example, by a vegetable tanning process (vegetable tanned crust stock). Suitable hides and skins that can be treated include, for example, bovine stock and sheep-skins.

Suitable basic salts of multivalent metals which can be used in the tanning process include particularly basic salts of metals having a valency of three or more, e.g. chromium, aluminium, zirconium and cerium. Salts of mineral acids are usually preferred, especially sulphuric acid. Particularly good results have been obtained using basic chromium sulphate, which can, for example, be prepared by adding sodium carbonate to a solution of chromium sulphate or chrome alum. The

basic salt of a multivalent metal may be masked with certain organic acid salts i.e. treated to form a mixed salt of modified reactivity but still capable of reacting with the organic compound.

The quantity of basic salt used is usually sufficient to give up to about 3.5% by weight (calculated as metal oxide) based on the dry weight of the hide or skin. Particularly good results have been obtained using a quantity of basic salt sufficient to give from 1.5 to 5.0% by weight of metal oxide based on the dry weight of the hide or skin.

The organic compound contains at least one and preferably two or more long chain aliphatic groups which preferably contain a chain of from six to thirtysix carbon atoms. Increasing the length of the aliphatic carbon chain or the number of aliphatic carbon chains in the compound is often found to give improved flexibility, perspiration resistance and water-shedding properties. The compound may contain one or more reactive groups which can, for example, be chloro, nitro, sulphonate, phosphate, carbonate, borate, citrate, thiocyanate, sulphate, amino or carboxyl groups.

Preferably the organic compound contains two or more reactive groups which for best results should be separated by a chain of at least six carbon atoms.

Mixtures of different organic compounds may be used provided that they do not react together and are stable under the reaction conditions.

Amongst many suitable organic compounds there may be mentioned alkali metal, ammonium or organic base salts of long chain aliphatic carboxylic acids for example, oleic, palmitic and stearic acids; half esters of long chain dicarboxylic acids; salts of sulphonated or sulphate long chain mono carboxylic acids, for example the ammonium, sodium and potassium salts of sulphonated or sulphated oleic and palmitic acids; sulphonated or sulphated triglycerides, for example medium sulphated cod oil, and lightly sulphated cold test neatsfoot oil; and long chain aliphatic amino acids.

The quantity of organic compound used is usually not less than 3% based on the shaved weight of the leather and is preferably from 3 to 8%. In many instances, it has been found useful in promoting penetration to carry out the reaction of the leather'with the organic compound in the presence of a water-soluble or water miscible alcohol or a liquid hydrocarbon. Suitable alcohols include benzyl alcohol and cyclohexanol, and suitable hydrocarbons include white spirit. After reaction with the organic compound, the leather is either further treated with a salt of a multivalent metal or dried to produce a crust stock.

The crust stock is easily wettable, and may similarly be converted to the waterproof state by treatment with a salt of a multivalent metal. This can be a basic salt, for example, the basic salt of chromium, aluminium, zirconium or cerium initially used for tanning or any other suitable basic salt, or a normal salt, for example, a copper, zinc, zirconium, aluminium or nickel salt, particularly a sulphate. This after-treatment confers the hydrophobic properties to the final product. The quantity of basic or normal salt used is usually such as to give from 1.0 to 3.0% by weight (calculated as metal oxide) based on the shaved weight of the leather. Prior to treatment with the salt of a multivalent metal the leather may be rinsed and lightly acidified on the outer surface to pH 4.6 to 5.0. the metal salt used may be masked" with a formate, acetate phthalate, citrate or other suitable salt.

The organic compounds used in the present invention do not usually form basic salts with multivalent metals which are soluble in water, and thus the tanning of the hide or skin with the basic salt of the multivalent metal and the treatment with the organic compound is preferably carried out by immersing the hide or skin in an aqueous solution of the basic salt of the multivalent metal, bringing the pI-I of the hide or skin in the reaction liquor up to the desired value and then adding the organic compound.

The process is preferably carried out in a tanning drum, since a low water/load ratio is desirable to accelerate the reactions. Suitable drum speeds have been found to be from 6 to 12 r.p.m., and an optimum speed can easily be found by experiment. The process may be completed in acceptable tannery time schedules and for each stage of the process the time for completion of the reaction is usually from 2 to 24 hours.

The reactions usually proceed at an acceptable rate at room temperature but if necessary elevated temperatures, for example up to about 50C, can be used.

Dyeing may be carried out prior to the further treat-, ment with a salt of a multivalent metal or subsequently. With some dyestuffs it is advisable to use a cold float.

After treatment by the process of the invention, the; leather may be neutralised if necessary and subjectedl to any of the normal finishing operations provided that the formulations used do not contain excessive amounts of surfactants or hydrophilic materials. The conventional fat-liquoring step can often be substantially reduced in amount and sometimes omitted altogether. Softer leathers are made by treating with a small amount of hydrocarbon solvent, e.g. white spirit, or a small amount of a straight oil e.g. neatsfoot or sperm oil emulsified in the organic reactants prior to application.

The invention is illustrated by the following Examples:

EXAMPLE 1 This Example describes a tanning process according. to the invention leading to the production of a leather having improved waterproofing properties.

A tanned chrome leather is prepared by treating pickled stock with from 1.5 to 3.5% by weight of chromic oxide in the form of a one-third basified chromium sulphate to a shrinkage temperature of about 100C. The leather is aged for twenty-four hours and freed from uncombined material by washing. After levelling the substance by splitting and/or shaving, the leather is placed in a water float in a tanning drum and the equilibrium pH raised to 7.5 to 9 with sodium bicarbonate OI ammonia.

In the same solution and at the same pI-I various organic compounds are added as detailed in Table l below until such time as complete penetration is obtained. This can be judged by a colour reaction on the cut edge with 5% w/w copper sulphate. When the liquor is exhausted and the penetration of the reactant found complete, the leather is washed thoroughly with water and the wash water drained off.

It is advisable at this stage to reduce the pH of the leather without disturbance of the unco-ordinated reactive groups in the leather. For this purpose a small amount of a weak acid or phthalic anhydride may be added using 5561]: 30 water as drum hast-rs;

about five minutes. In this manner the surface pH of the leather is reduced to about 4.6. At the same time or immediately afterwards 5% of a neutral salt such as sodium sulphate is added to restrain the rate of subsequent re-tannage.

The leather is then treated with a further 6 to 8% by weight of basic chromium sulphate powder (containing 24 to 26 by weight of Cr O to produce a hydrophobic leather. After complete penetration as tested by an indicator such as bromocresol green, the resultant leather is washed free of electrolytes and dried out.

The results are given in Table I. Water-proofing is judged by SLP22 (IUP/lO) which is the accepted test of the International Union of Leather Chemists Societies. This is expressed as the time taken for water'to penetrate the sample and the amount of water taken up expressed as a percentage of the sampleweight. In the result a running period of 240 minutes is taken as evidence of water-proofing and figures quoted at less than 240 minutes indicate that the leather had wet through.

The amounts of organic compounds are given as percentages of the shaved or split weight of the wet chrome leather containing approximately water.

TABLE I Dynamic water uptake (DWU) time H Compound age pH (minutes) absor d l. Ammonium oleate 3 8.2 150 30 2. Ammonium salt of sulphated oleic acid 4 8.5 23

6 8.5 270 26 (as above but degreased) 4 8.5 180 25 v 3. Ammonium salt of sul ated oleic acid 6 7.5 120 (di erent source) 6 8.5 210 35 y 4. Potassium salt of sulphated oleic acid 6 7.5 97

i i 6 TA LE 1 Continued 7 Dynamic water uptake (DWU) I time H O Compound age pl-l (minutes) absorbed 5. Sulphated oleic acid sodium finish 80% approx. 6 8.2 8.4 240 13 8 8.2 8.4 240 I9 as above but with 5% benzyl alcohol 6 8.2 8.4 240 12 8 8.2 8.4 240 12 6. Medium sulphated cod oil 80% 2 8.2 8.4 70 18 4 8.2 8.4 165 18 8.2 8.4 240 22 7. Lightly sulphated cold test neatsfoot oil 85% 4 8.2 8.4 120 aism ia's is as areas side (bovineitochl All other experiments are on chromed sheep skins. Con- EXAMPLE 2 This Example describes further processes according to the invention for the production of a leather having improved water-proofing properties.

The procedure of Example 1 is repeated except the leather is neutralised to a pH of 8.2 to 8.4 prior to the 'application of the organic compound. Re-tannage is carried out using a mixture of 5% sodium sulphate and 6% basic 33% chromium sulphate powder (25% (Ir- G based on the shaved weight of the leather or 6% basic aluminium chloride (66% basic) 25% A1 0 In each case, half of the samples were degreased with petroleum ether. The results are given in Table 11. Percentages of organic compounds used are based on the shaved weight of the leather containing 60 65% water.

imaaaetar Cassia; with the basiatama altar; multivalent metal, and thirdly treating the hide or skin with a salt of a multivalent metal at an acid pH.

20 2. A process according to claim 1, in which the treatment with the organic compound is carried out at a pH of from 7.5 to 9.

3. A process according to claim 2, in which the required pH is maintained by addition of a weak alkali.

25 4. A process according to claim 1, in which the leather is washed and neutralised throughout its whole thickness after tanning with the basic tanning salt of a multivalent metal and prior to treatment with the organic compound.

5. A process according to claim I, in which the basic tanning salt of a multivalent metal is a basic salt of chromium, aluminum, zirconium or cerium.

6. A process according to claim 1, in which the basic tanning salt is a mineral acid salt.

7. A process according to claim 1, in which the quantity of the basic tanning salt of a multivalent metal used is sufficient to give from 1.5 to 5.0% by weight of metal oxide based on the dry weight of the hide or skin.

8. A process according to claim 1, in which the long chain aliphatic group contains a chain of from si-x to 36 carbon atoms.

9. A process according to claim 8, in which the or- TABLE II Re-tannage Compound Chrome Aluminium DWU DWU DWU DWU Degreased Degreased time H O time l-1 O time H O time H O (minutes) absorbed (minutes) absorbed (minutes) absorbed (minutes) absorbed Ammonium oleate 4% 300+ 19 240+ 16 270+ 6% 240+ 19 240+ 19 180+ 5 l 270+ 58 Sulphated cod oil 6% 210 24 18(H 14 126 270 39 Sulphated neatsfoot oil 6% 60 l l 22 60 24 270+ 41 mira e resiilts'sliow that both'ciir'oiiiiiirfi mamas?" 'igafiii: compound is ohe that contains two or more lo ng chain aliphatic groups.

" lli K i'dcsidcifiih to claim fiiwhich the re active group of the organic compound is a chloro, ni-" tro, sulphonate, phosphate, carbonate, borate, citrate, thiocyanate, sulphate, amino or carboxyl group.

llTA process a'ccaraiag to claim lriii which the organic compound contains two or more reactive groups separated by a chain of at least six carbon atoms.

"izfKbrace's'ccaiiiihg to claim 1, in which the organic compound is an alkali metal, ammonium or organic base salt of a long chain aliphatic carboxylic acid, a half ester of a long chain aliphatic dicarboxylic acid,

a salt of a sulphonated or sulphated long chain mono hol or a liquid hydrocarbon.

15. A process according to claim 1, in which the hide or skin is immersed in an aqueous solution of the basic tanning salt of the multivalent metal, the pH of the hide or skin in the aqueous solution is brought up to the desired value, and the organic compound is then added.

16. A process according to claim 1, in which after treatment with the organic compound, the hide or skin is further treated with a basic salt of a multivalent metal.

17. A process according to claim 16, in which the basic salt of a multivalent metal that is used to further treat the hide or skin is a basic salt of chromium, aluminum, zirconium or cerium.

18. A process according to claim 16, in which the quantity of basic salt used for the further treatment is from 1.0 to 3.0% by weight, calculated as metal oxide, based on the shaved weight of the leather.

19. A process according to claim 1, in which, after treatment with the organic compound, the hide or skin is further treated with a normal salt of amultivalent metal.

20. A process according to claim 19, in which the normal salt is a salt of copper, zinc, zirconium, aluminium or nickel. I

21. A process according to claim 19, in which the quantity of normal salt used for the further treatment is from 1.0 to 3.0% by weight, calculated as metal oxide, based on the shaved weight of the leather.

22. A leather tanned with a basic tanning salt of a multivalent metal and containing on adsorbed complex of an organic compound, having a long chain aliphatic group and a single reactive group, and a salt of a multivalent metal, said leather being produced by the process of claim 1.

23. A leather according to claim 22, in which the basic tanning salt of a multivalent metal is a basic salt of chromium, aluminium, zirconium or cerium.

24. A leather according to claim 22, in which the organic compound is an alkali metal, ammonium or organic base salt of a long chain aliphatic carboxylic acid, a half ester of a long chain dicarboxylic acid, or a long chain aliphatic amino acid.

25. A leather according to claim 22, in which the salt of a multivalent metal thatis used to further treat the leather is a basic salt of chromium, aluminium, zirconium or cerium. 26. A leather according to claim 22, in which the salt of a multivalent metal that is used to further treat the leather is a normal salt of copper, zinc, zirconium, aluminium or nickel.

27. A leather tanned with a basic tanning salt of a multivalent metal and containing chemically bonded residues of a complex of an organic compound, having a long chain aliphatic group and two or more reactive groups, and a salt of a multivalent metal, said leather being produced by the process of claim 1.

28. A leather according to claim 27, in which the basic tanning salt of a multivalent metal isa basic salt of chromium, aluminium, zirconium or cerium.

29. A leather according to claim 27, in which the organic compound is a salt of a sulphonated or sulphated long chain mono carboxylic acid, or a sulphonated or sulphated trigylceride.

30. A leather according to claim 27, in which the salt of a multivalent metal that is used to further treat the leather is a basic salt of chromium, aluminium, zirconium or cerium.

31. A leather according to claim 27, in which the salt of a multivalent metal that is used to further treat the leather is a normal salt of copper, zinc, zirconium, aluminium or nickel. 

1. A process for the tanning of a hide or skin which comprises firstly treating the hide or skin with a basic tanning salt of a multivalent metal, secondly treating the hide or skin with an organic compound having a long chain aliphatic group while maintaining alkaline pH conditions during such treatment said compound having at least one reactive group capable of entering into a metal complex with the basic tanning salt of a multivalent metal, and thirdly treating the hide or skin with a salt of a multivalent metal at an acid pH.
 1. A PROCESS FOR THE TANNING OF A HIDE OR SKIN WHICH COMPRISES FIRSTLY TREATING THE HIDE OR SKIN WITH A BASIC TANNING SALT OF A MULTIVALENT METAL, SECONDLY TREATING THE HIDE OR SKIN WITH AN ORGANIC COMPOUND HAVING A LONG CHAIN ALIPHATIC GROUP WHILE MAINTAINING ALKALINE PH CONDITIONS DURING SUCH TREATMENT SAID COMPOUND HAVING AT LEAST ONE REACTIVE GROUP CAPABLE OF ENTERING INTO A METAL COMPLEX WITH THE BASIC TANNING SALT OF A MULTIVALENT METAL, AND THIRDLY TREATING THE HIDE OR SKIN WITH A SALT OF A MULTIVALENT METAL AN ACID PH.
 2. A process according to claim 1, in which the treatment with the organic compound is carried out at a pH of from 7.5 to
 9. 3. A process according to claim 2, in which the required pH is maintained by addition of a weak alkali.
 4. A process according to claim 1, in which the leather is washed and neutralised throughout its whole thickness after tanning with the basic tanning salt of a multivalent metal and prior to treatment with the organic compound.
 5. A process according to claim 1, in which the basic tanning salt of a multivalent metal is a basic salt of chromium, aluminium, zirconium or cerium.
 6. A process according to claim 1, in which the basic tanning salt is a mineral acid salt.
 7. A process according to claim 1, in which the quantity of the basic tanning salt of a multivalent metal used is sufficient to give from 1.5 to 5.0% by weight of metal oxide based on the dry weight of the hide or skin.
 8. A process according to claim 1, in which the long chain aliphatic group contains a chain of from six to 36 carbon atoms.
 9. A process according to claim 8, in which the organic compound is one that contains two or more long chain aliphatic groups.
 10. A process according to claim 1, in which the reactive group of the organic compound is a chloro, nitro, sulphonate, phosphate, carbonate, borate, citrate, thiocyanate, sulphate, amino or carboxyl group.
 11. A process according to claim 1, in which the organic compound contains two or more reactive groups separated by a chain of at least six carbon atoms.
 12. A process according to claim 1, in which the organic compound is an alkali metal, ammonium or organic base salt of a long chain aliphatic carboxylic acid, a half ester of a long chain aliphatic dicarboxylic acid, a salt of a sulphonated or sulphated long chain mono carboxylic acid, a sulphonated or sulphated triglyceride, or a long chain aliphatic amino acid.
 13. A process according to claim 1, in which the quantity of organic compound used is from 3 to 8% based on the shaved weight of the leather.
 14. A process according to claim 1, in which the treatment with the organic compound is carried out in the presence of a water-soluble or water miscible alcohol or a liquid hydrocarbon.
 15. A process according to claim 1, in which the hide or skin is immersed in an aqueous solution of the basic tanning salt of the multivalent metal, the pH of the hide or skin in the aqueous solution is brought up to the desired value, and the organic compound is then added.
 16. A process according to claim 1, in which after treatment with the organic compound, the hide or skin is further treated with a basic salt of a multivalent metal.
 17. A process according to claim 16, in whiCh the basic salt of a multivalent metal that is used to further treat the hide or skin is a basic salt of chromium, aluminum, zirconium or cerium.
 18. A process according to claim 16, in which the quantity of basic salt used for the further treatment is from 1.0 to 3.0% by weight, calculated as metal oxide, based on the shaved weight of the leather.
 19. A process according to claim 1, in which, after treatment with the organic compound, the hide or skin is further treated with a normal salt of a multivalent metal.
 20. A process according to claim 19, in which the normal salt is a salt of copper, zinc, zirconium, aluminium or nickel.
 21. A process according to claim 19, in which the quantity of normal salt used for the further treatment is from 1.0 to 3.0% by weight, calculated as metal oxide, based on the shaved weight of the leather.
 22. A LEATHER TANNED WITH A BASIC TANNING SALT OF A MULTIVALENT METAL AND CONTAINING ON ADSORBED COMPLES OF AN ORGANIC COMPOUND, HAVING A LONG CHAIN ALIPAHTIC GROUP AND A SINGLE REACTIVE GROUP, AND A SLAT OF A MULTIVALENT METAL, SAID LEATHER BEING PRODUCED BY THE PROCESS OF CLAIM
 1. 22. A leather tanned with a basic tanning salt of a multivalent metal and containing an adsorbed complex of an organic compound, having a long chain aliphatic group and a single reactive group, and a salt of a multivalent metal, said leather being produced by the process of claim
 1. 23. A leather according to claim 22, in which the basic tanning salt of a multivalent metal is a basic salt of chromium, aluminium, zirconium or cerium.
 24. A leather according to claim 22, in which the organic compound is an alkali metal, ammonium or organic base salt of a long chain aliphatic carboxylic acid, a half ester of a long chain dicarboxylic acid, or a long chain aliphatic amino acid.
 25. A leather according to claim 22, in which the salt of a multivalent metal that is used to further treat the leather is a basic salt of chromium, aluminium, zirconium or cerium.
 26. A leather according to claim 22, in which the salt of a multivalent metal that is used to further treat the leather is a normal salt of copper, zinc, zirconium, aluminium or nickel.
 27. A leather tanned with a basic tanning salt of a multivalent metal and containing chemically bonded residues of a complex of an organic compound, having a long chain aliphatic group and two or more reactive groups, and a salt of a multivalent metal, said leather being produced by the process of claim
 1. 28. A leather according to claim 27, in which the basic tanning salt of a multivalent metal is a basic salt of chromium, aluminium, zirconium or cerium.
 29. A leather according to claim 27, in which the organic compound is a salt of a sulphonated or sulphated long chain mono carboxylic acid, or a sulphonated or sulphated triglyceride.
 30. A leather according to claim 27, in which the salt of a multivalent metal that is used to further treat the leather is a basic salt of chromium, aluminium, zirconium or cerium. 